Control of aphids and whiteflies (Homoptera: Aphididae and Aleyrodidae) with different Neem preparations in laboratory, greenhouse and field:: effects and limitations

Three neem preparations were tested with whiteflies: Neemoil (NO), NeemAzal-T/S(R) (NA), and Neem Kernel Water Extract (NKWE). NA and NKWE in different concentrations were tested also with five aphid species. Most studies took place in the laboratory and in the greenhouse, but two field experiments were conducted in Germany (with Brevicoryne brassicae) and in Panama (with Bemisia tabaci). NO, containing a low concentration of Azadirachtin A (AzaA), and NKWE affected the egg hatching in Trialeurodes vaporariorum, in contrast to NA. All preparations induced a significant mortality in whitefly nymphs. NA also affected their puparia. The formulation of NA contributed to these effects. In Myzus persicae, Lipaphis erysimi and B. brassicae, the spraying of cabbage leaves with NKWE had more severe effects on nymphs than spraying the nymphs themselves topically (mortality and fecundity of survivors). The spraying of adult aphids topically with NKWE showed only effects in case of very high concentrations of AzaA. Vicia faba was shown to take up AzaA from the soil, when NKWE had been applied, with a maximum concentration in leaves after 5 days. The attack by Aphis fabae on such plants started declining after 5 days. AzaA is not only taken up by the plant roots, but also through the plant cuticle, as an experiment with Acyrtosiphon pisum on V faba showed. When aphid nymphs were transferred to cabbage plants at different days after soil treatment with NKWE, mortality and fecundity of survivors proved to be severely affected up to 10 days (except L. eysimi: 8 days). In a cabbage field in Germany, NKWE in high concentrations reduced the attack by B. brassicae only with a delay of 2 days (in which time pirimicarb had killed 100 %). In tomatoes in Panama, the effect of weekly applications of NA (and of endosulfan) on the attack by B. tabaci was weak. The infection with gemini-viruses by B. tabaci could not be reduced (in contrast to imidacloprid with 3-weekly applications). The tomato yield was significantly lowest in the NA-plots. The significance of the different results obtained for neem use is discussed.